1. Field of the Invention
The present invention pertains in general to friction clutches and to torque-detecting arrangements and wear-detecting arrangements provided for such clutches.
2. Description of the Related Art
Modern drive systems frequently make use of friction clutches, which are no longer operated directly by mechanical means by the driver, but rather by an actuator. So that the clutch-engaging and clutch-disengaging operations can be carried out properly, it is necessary for various parameters which characterize the operating state of this type of friction clutch to be known. Thus, for example, it is necessary especially for the sake of synchronization with the shifting operations which take place in the transmission system to know the exact degree to which the clutch is engaged or disengaged at the moment in question. This is usually done by measuring the release distance, and on the basis of the release distance, a conclusion can ultimately be drawn concerning the amount of torque being transmitted via the clutch. Because in this case a chain of mechanically interacting components is involved, all of which have manufacturing tolerances and all of which can have a certain amount of play with respect to each other, this type of detection method suffers from a comparatively high degree of uncertainty, as a result of which it is difficult to determine the exact extent to which the clutch is engaged or disengaged at a specific moment. Here, too, the state of wear, such as the degree to which the friction linings present in a friction clutch have been worn down, also exerts a considerable influence on the engaging and disengaging characteristic. When wear of this kind occurs, a stored-energy device present in the clutch usually also changes its installation position and thus its force characteristic as well, which means that the time it takes for the various engaging and disengaging operations to occur can also change unless appropriate adjustments are made to the control measures for the actuator.
A system is also known from the U.S. published Application No. 2002/096,416, in which, to detect the torque being transmitted by a friction clutch, a sensor is used to scan a code provided on the transmission input shaft. This code is formed by the appropriate magnetization of the shaft, and a sensor signal is generated by the twisting of the shaft which occurs during the torque-transmitting process and by the associated change in the area of the code. This signal is ultimately related to the torque transmitted by the clutch and can be used to ensure that the actuator actuates the clutch properly.